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Register a new userA Uniformly Selected Sample of Low-Mass Black Holes in Seyfert 1 Galaxies. II. The SDSS DR7 Sample
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A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20) * 10^5 M_sun. The AGNs are selected from a systematic search among galaxies in the Seventh Data Release (DR 7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from the SDSS DR 4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed, in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [O III] luminosity. The effective optical-to-X-ray spectral indices alpha_OX, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500AA. Interestingly, a correlation of alpha_OX with black hole mass is also found in the sense that alpha_OX is statistically flatter (stronger X-ray relative to optical) for lower black hole mass. Only 26 objects, mostly radio loud, were detected in radio at 20 cm in the FIRST survey, giving a radio loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8-10^12.4 M_sun and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone a continuous star formation history.
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We present an expanded sample of low-mass black holes (BHs) found in galactic nuclei. Using standard virial mass techniques to estimate BH masses, we select from the Fourth Data Release of the Sloan Digital Sky Survey all broad-line active galaxies with masses < 2 x 10^6 M_sun. BHs in this mass regime provide unique tests of the relationship between BHs and galaxies, since their late-type galaxy hosts do not necessarily contain classical bulges. Furthermore, they provide observational analogs of primordial seed BHs and are expected, when merging, to provide strong gravitational signals for future detectors such as LISA. From our preliminary sample of 19, we have increased the total sample by an order of magnitude to 174, as well as an additional 55 (less secure) candidates. The sample has a median BH mass of <M_BH> = 1.3 x 10^6 M_sun, and in general the objects are radiating at high fractions of their Eddington limits. We investigate the broad spectral properties of the sample; 55 are detected by rosat, with soft X-ray luminosities in the range 10^40 to 7 x 10^43 ergs/sec. Much like the preliminary sample, these objects are predominantly radio-quiet (R = f_6cm/f_4400A < 10), but 11 objects are detected at 20 cm, with radio powers (10^21-10^23 W/Hz) that may arise from either star formation or nuclear activity; only 1% of the sample is radio-loud. We further confirm that, with <M_g>=-19.3 and <g-r> = 0.7 mag, the host galaxies are low-mass, late-type systems. At least 40% show disk-like morphologies, and the combination of host galaxy colors and higher-order Balmer absorption lines indicate intermediate-age stellar populations in a subset of the sample.
Narrow line Seyfert 1 galaxies (NLS1s) are believed to be powered by accretion of matter onto low mass black holes (BHs) in spiral host galaxies with BH masses M_BH of 10^6 - 10^8 M_sun . However, the broad band spectral energy distribution of the gamma-ray emitting NLS1s are found to be similar to flat spectrum radio quasars. This challenges our current notion of NLS1s having low M_BH . To resolve this tension of low M_BH values in NLS1s, we fitted the observed optical spectrum of a sample of radio-loud NLS1s (RL-NLS1s), radio-quiet NLS1s (RQ-NLS1s) and radio-quiet broad line Seyfert 1 galaxies (RQ-BLS1s) of about 500 each with the standard Shakura-Sunyaev accretion disk (AD) model. For RL-NLS1s we found a mean log(M_ADBH/M_sun) of 7.98 +/- 0.54. For RQ-NLS1s and RQ-BLS1s we found mean log(M_ADBH/M_sun) of 8.00 +/- 0.43 and 7.90 +/- 0.57, respectively. While the derived M_BH values of RQ-BLS1s are similar to their virial masses, for NLS1s the derived M_ADBH values are about an order of magnitude larger than their virial estimates. Our analysis thus indicates that NLS1s have M_BH similar to RQ-BLS1s and their available virial M_BH values are underestimated influenced by their observed relatively small emission line widths. Considering Eddington ratio as an estimation of the accretion rate and using M_ADBH, we found the mean accretion rate of our RQ-NLS1s, RL-NLS1s and RQ-BLS1s as 0.06 (+0.16, -0.05), 0.05 (+0.18, -0.04) and 0.05 (+0.15, -0.04) respectively. Our results therefore suggest that NLS1s have BH masses and accretion rates similar to BLS1s.
We present a sample of $X$-ray selected candidate black holes in 51 low mass galaxies with $zle 0.055$ {and mass up to $10^{10}$ M$_{odot}$} obtained by cross-correlating the NASA-SLOAN Atlas with the 3XMM catalogue. {We have also searched in the available catalogues for radio counterparts of the black hole candidates and find that 19 of the previously selected sources have also a radio counterpart.} Our results show that about $37%$ of the galaxies of our sample host { an $X$-ray source} (associated to a radio counterpart) spatially coincident with the galaxy center, in agreement with { other recent works}. For these {it nuclear} sources, the $X$-ray/radio fundamental plane relation allows one to estimate the mass of the (central) candidate black holes which results to be in the range $10^{4}-2times10^{8}$ M$_{odot}$ (with median value of $simeq 3times 10^7$ M$_{odot}$ and eight candidates having mass below $10^{7}$ M$_{odot}$). This result, while suggesting that $X$-ray emitting black holes in low-mass galaxies may have had a key role in the evolution of such systems, makes even more urgent to explain how such massive objects formed in galaxies. {Of course, dedicated follow-up observations both in the $X$-ray and radio bands, as well as in the optical, are necessary in order to confirm our results
The study of narrow-line Seyfert 1 galaxies (NLS1s) is now mostly limited to low redshift ($z<0.8$) because their definition requires the presence of the H$beta$ emission line, which is redshifted out of the spectral coverage of major ground-based spectroscopic surveys at $z>0.8$. We studied the correlation between the properties of H$beta$ and Mg II lines of a large sample of SDSS DR14 quasars to find high-$z$ NLS1 candidates. Based on the strong correlation of $mathrm{FWHM(MgII)=(0.880pm 0.005) times FWHM(Hbeta)+ (0.438pm0.018)}$, we present a sample of high-$z$ NLS1 candidates having FWHM of Mg II $<$ 2000 km s$^{-1}$. The high-$z$ sample contains 2684 NLS1s with redshift $z=0.8-2.5$ with a median logarithmic bolometric luminosity of $46.16pm0.42$ erg s$^{-1}$, logarithmic black hole mass of $8.01pm0.35 M_{odot}$, and logarithmic Eddington ratio of $0.02pm0.27$. The fraction of radio-detected high-$z$ NLS1s is similar to that of the low-$z$ NLS1s and SDSS DR14 quasars at a similar redshift range, and their radio luminosity is found to be strongly correlated with their black hole mass.
We revisited the spectroscopic characteristics of narrow-line Seyfert 1 galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7) public archive. We confirm that NLS1s are mostly characterized by Balmer lines with Lorentzian profiles, lower black hole masses and higher Eddington ratios than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common properties. Strong Fe II emission does not seem to be a distinctive property of NLS1s, as low values of Fe II/H$beta$ are equally observed in these AGNs. Our data indicate that Fe II and Ca II kinematics are consistent with the one of H$beta$. On the contrary, O I $lambda$8446 seems to be systematically narrower and it is likely emitted by gas of the broad-line region more distant from the ionizing source and showing different physical properties. Finally, almost all NLS1s of our sample show radial motions of the narrow-line region highly-ionised gas. The mechanism responsible for this effect is not yet clear, but there are hints that very fast outflows require high continuum luminosities (> $10^{44}$ erg/s) or high Eddington ratios (log(L$_{rm bol}$/L$_{rm Edd}$) > -0.1).
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